In many devices and manufacturing processes it can desirable to sense the characteristics of a material present in a container, or other type enclosure. For example, it may be desirable to detect the amount of space occupied by a material, such as the level of liquid within a container.
Conventional approaches to determining liquid levels have included mechanical devices. For example, floats have been employed that can actuate a switch to signal when a particular level has been reached. A drawback to such mechanical approaches can be limited reliability. Mechanical connections may freeze or otherwise malfunction for a variety of reasons, such as corrosion, lack of lubrication and wear. Further, to ensure proper operations mechanical switches can require ongoing maintenance, which can add to the cost of ownership for such devices or systems.
Capacitance sensing systems are known that can sense a level of a liquid within a container. Such conventional approaches can include a plate positioned on an inside surface or outside surface of a container. A capacitance presented by the plate can increase as the container volume occupied by a liquid increases, and vice versa. However, such a conventional approach can suffer from accuracy, as a sensed capacitance value can change according to environmental conditions, such as temperature. This can be a particular problem for sensing predetermined limits (i.e., almost empty or almost full), as such a limit value can change according to environment.
One very particular example of such a limit sensing difficulty can be with humidifier systems. Some conventional humidifier systems can include a reservoir having a heating element situated at the bottom. The reservoir can be filled with water and the heating element activated to evaporate the water. The heating element can be damaged, or its operating lifetime reduced if it is activated (is heating) while exposed to air. Thus, a water level sensor is needed in such to ensure the heating element is turned off while it is still submerged, or if no water is in the reservoir.